Device and method for reproducing photographic sound recordings

ABSTRACT

For a reproduction of optical sound information in a double variable-area track (DZ) an optoelectronic converter device scans the optical sound track of a film. The converter device generates a digital image signal for buffer storage in the memory of a program-controlled data processing device. The data processing device derives the profile of the two edges of the double variable-area track from data values of the buffer-stored image signal. Audio data for a sound reproduction are generated using data about the edge profile determined.

This application claims the benefit under 35 U.S.C. § 365 ofInternational Application PCT/EP01/09686 filed Aug. 22, 2001, whichclaims the benefit of German Application No. 10044978.6, filed Sep. 11,2000.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for the reproduction of opticalsound recordings, which has an optoelectronic converter device for theoptical scanning of an optical sound track, which outputs a digitalimage signal of the scanned optical sound track at an output, and whichcontains a device for buffer-storing the image signal output by theconverter device. Furthermore, the invention relates to a method for thereproduction of optical sound recordings, in particular optical soundrecordings in which the sound information is recorded as a doublevariable-area track on film.

In the case of 35 mm cinema films, the sound information is recorded onan optical sound track which is located between image information andlateral perforation holes. For the reproduction of the soundinformation, the film is transported at a speed of 24 frames per second.While the film is being transported, a light beam illuminates theoptical sound track. The light beam is modulated by transparencydifferences in the scanned optical sound track and directed onto alight-sensitive sensor. For loudspeaker reproduction, the analogue soundsignal output by the light-sensitive sensor is amplified.

There are various optical sound tracks. In the case of the so-calledvariable-density track, the transparency of the optical sound track isproportional to the recorded modulation amplitude. In the case of theso-called double variable-area track, the width of the clear area isproportional to the modulation amplitude of the sound signal.

Older films that are frequently used often exhibit two types of error:one type involves dirt and dust on the surface of the film; the othertype involves scratches in the running direction of the film, so-calledrunning scratches, which are caused by mechanical contact of the filmguiding elements with the film surface. Optical sound tracks areparticularly sensitive to disturbances caused by dirt and scratches, thenumber of which rises with the number of times that the film copy isprojected. Distortions of speech sibilants, a so-called thunder effect,can arise as a result of scattered light effects of the variable-areatrack.

In order to restore old cinema films, nowadays the image part is copiedonto a new film carrier and the optical sound track is transferred to amagnetic film in single-track fashion in order to prevent the soundtracks that are often scratched and in part disturbed by dirt from beingtransferred to the new film carrier as a result of optical copying ofthe optical sound tracks. Furthermore, sound post-processing withelectronic filters and manual processing is used in an attempt to removeclicks and crackling from the original sound.

DE 197 29 201 A1 has already described a film scanner with a device forscanning optical sound tracks on a tape-type carrier, in the case ofwhich the sound information is scanned perpendicularly to the directionof movement of the carrier by an opto/electronic converter device. Theopto/electronic converter device scans the sound information line byline in order to generate samples for a digital two-dimensionalfiltering. In this case, the optical sound tracks can be scanned by aCCD line sensor or by a light spot for the control of a photosensor,which light spot is directed transversely over the sound tracks.

U.S. Pat. No. 4,124,784 A discloses an apparatus for the reproduction ofoptical sound recordings in which the edge of the optical sound track isscanned. An analogue scanning signal filtered in a suitable manner formsthe basis for the signal processing. The purpose of the apparatus is toimprove the sound signal and to reduce noise.

DE 19 737 570 A discloses an archiving system for cinematographic filmmaterial with a film scanner. The film scanner optically scans the imageinformation and an image sound track. The image data are stored indigitized form without further processing. Sound and image signals arereproduced as separate data signals.

SUMMARY OF THE INVENTION

The present invention is based on the object of providing an apparatusand a method for the reproduction of optical sound recordings of thetype mentioned in the introduction, which makes it possible to eliminatedisturbances.

This object is achieved according to the invention by means of anapparatus for the program-controlled data processing of thebuffer-stored image signal, which firstly determines the profile ofedges of a variable-area track from data values of the image signal andwhich then generates audio data for a sound reproduction from data ofthe edge profile determined.

The invention has the advantage that the digital image signal generatedby scanning an optical sound track can be examined using digital imageprocessing means. Sound information which has been recorded as a single,double or multiple variable-area track on the sound track of a film cannow be subjected to

-   -   error concealment and/or error correction beforehand—before the        sound information is present as useful information—, the image        information on the sound track, rather than the sound        information per se, being examined and subjected to error        concealment and/or error correction.

In one embodiment of the invention, it is provided that the data valuesof pixels of the buffer-stored image signal, representing brightnessvalues, are subjected to a filtering in a program-controlled manner overthe duration of a plurality of lines. Brightness values of the pixelscan be changed according to a predetermined function, e.g. according toa linear or a nonlinear transfer function. Very bright pixels can befiltered out or bright and dark pixels can be compressed in thebrightness range. The filtering makes it possible to steepen the suddenbrightness changes at the optical sound edges of a variable-area track.The dynamic range is optimized by a normalization filter. By checking anumber of lines, the data values for black (maximum film density) arecorrected to 0% and the data values for white (minimum film density) to100% of the range of brightness values.

In the case of the variable-area track, the width of the transparentarea on the optical sound track of a film is proportional to themodulation amplitude of the recorded sound signal. Therefore, for thereproduction of a sound information item recorded in the variable-areatrack, it is of crucial importance to determine the profile of theboundary-of the transparent area, i.e. the edge profile of thevariable-area track.

In an advantageous embodiment of the invention, in order to determinethe edge profile of a double variable-area track, it is proposed that,in a first step, in a program-controlled manner, the position of edgeboundaries running transversely with respect to the longitudinaldirection of the film is determined using the position of suddenbrightness changes in the line profile by evaluation of the data valuesof the pixels representing brightness values, that, in a second step, atrack centre running between the edge boundaries determined iscalculated, and that, in a third step, the buffer-stored pixel data aremirrored at the calculated track centre, thereby producing pixel data ofa single variable-area track. The symmetry property of the doublevariable-area track is advantageously utilized in this case.

In accordance with one development of the invention, the program of adata processing device is created such that, during the evaluation ofpixel data of a double variable-area track the position region of thetrack centre is limited by setting an upper and lower threshold. Inanother development, the profile of edge boundaries determined and/orthe profile of the track centre is smoothed according to a predeterminedfunction.

As mentioned in the introduction, the double variable-area trackrecorded on the sound track of a film may have errors. According to anembodiment of the invention, a program of the data processing device hasat least one test routine for detecting errors in a double variable-areatrack. A simple test routine consists in an overshooting of the upperand/or lower threshold of the position region of the track centredetermined being assessed as an error in the edge profile of the doublevariable-area track. Another test routine-provides for the overshootingof a specific boundary in the edge profile of the double variable-areatrack being assessed as an error in the edge profile of the doublevariable-area track.

In order to conceal errors identified in the image of the examineddouble variable-area track, the program of the data processing devicehas at least one routine for concealing errors in a double variable-areatrack. In this case, the program is configured in such a way that apixel value that has been identified as erroneous is replaced by thepixel value of a preceding line. If the two edge pixels cannot be foundwithin a line due to image errors, the pixel values of the precedingline should serve as replacement pixels.

Another advantageous solution consists in creating the program of thedata processing device such that data values of pixels identified aserroneous between the edge boundaries of the double variable-area trackare replaced by predetermined data values, for example by data valuescorresponding to black pixels. The data values of pixels identified aserroneous which are located outside the edge boundaries of the doublevariable-area track are to be replaced by data values corresponding to agrey pixel.

Furthermore, it is advantageous to configure the program of the dataprocessing device such that when errors are detected in pixels outsidethe edge boundaries of a double variable-area track the data value of anerroneous pixel is replaced by a data value determined byautocorrelation. Completely destroyed sound track regions at splices inthe film or at locations at which there are so-called sound flies on thefilm can be regenerated—at least in part—by extrapolation. The severeclick disturbances audible at splices and the sound dropouts audible inthe case of sound flies can be alleviated.

Erroneous pixels identified in segments of the edge profiles canadvantageously be calculated according to an autocorrelation function inaccordance with the following algorithm:

${a_{before}(n)} = {\frac{1}{a(0)}*\underset{i = 0}{\overset{N - 1}{å}}{g( {y - i} )}*{g( {y - i - n} )}}$

-   -   where        -   g(y) is a grey-scale value,        -   y is a line number,        -   i is a running index from 0 to N−1,        -   n is a variable of the autocorrelation function where n=0 to            N−1,        -   N is the number of undisturbed lines to be used for            restoration.

Erroneous pixels are then to be replaced by grey-scale value pixelswhose position within a line satisfies the following function:

${g(z)} = {{\frac{Z + 1 - z}{Z + 1}*{g( {Z - P_{before}} )}} + {\frac{z}{Z + 1}*{g( {z + P_{after}} )}}}$

-   -   where        -   g(z) denotes a grey-scale value to be replaced,        -   Z denotes the number of lines to be replaced,        -   z denotes the line number, 1≦z≦Z.        -   P_(before) and P_(after) denote the periodicities in sound            tracks before and, respectively, after a detected error.

One development of the invention comprises a method for the reproductionof optical sound recordings, in which a digital image signal isgenerated by scanning an optical sound track, in which data of the imagesignal generated are buffer-stored, in which an edge profile of avariable-area track recorded on the optical sound track is determined ina manner dependent on values of the buffer-stored data, and in whichcorresponding audio data for a sound reproduction are derived in amanner dependent on the edge profile determined.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described and explained in more detail usingexemplary embodiments illustrated in the drawings, in which:

FIG. 1 shows an optical scanning device for optical sound tracks andalso a block diagram for the processing of image data of the scannedoptical sound tracks in accordance with the invention,

FIG. 2 shows the diagrammatic illustration of a 35 mm cinema film,

FIG. 3 shows the enlarged illustration of an optical sound track in adouble variable-area track,

FIG. 4 shows a flow diagram for the image processing of optical soundinformation in a double variable-area track,

FIG. 5 shows the enlarged illustration of an image-processed doublevariable-area track.

Identical parts bear identical reference symbols in the figures.

DETAILED DESCRIPTION

In FIG. 1, 1 designates an illumination source. The light from theillumination source 1 radiates onto an optical sound track 3 of a film 4via a first condenser 2.

FIG. 2 shows the position of the optical sound track 3 on a 35 mm cinemafilm 4. In the case of the 35 mm cinema film, the optical sound track 3has a track width of 2.5 mm. The optical sound track 3 is located on oneside between film image windows 5 having a width of 22 mm and a firstperforation track 6. A second perforation track 7 runs on the other sideof the film image windows 5. The perforation tracks 6 and 7 are providedfor transporting the film; they have perforation holes P. The imageheight of a 35 mm cinema film is 16 mm; the image position has 19 mm.The film image windows 5 are separated by frame lines 7 in thelongitudinal direction of the film 4.

A detail from the optical sound track 3 is shown enlarged in FIG. 3. Itshall be assumed that the optical sound track 3 contains, as opticalsound information, a double variable-area track DZ with pure tonecontrol RB. The double variable-area track DZ extends in thelongitudinal direction of the film 4 as a blackened track. As mentionedin the introduction, in the case of the double variable-area track DZthe width of the clear area is proportional to the modulation amplitudeof a recorded sound signal.

The film is transported through two toothed rollers 9 and 10, whichengage in perforation holes P in the perforation tracks 6 and 7 runninglaterally with respect to the film 4. The toothed rollers 9 and 10 areoperatively connected to motors (not illustrated) whose rotational speedis regulated by a film transport servo 11. The transport speed of a 35mm cinema film is 24 frames per second (=45.6 cm/s).

Arranged on the opposite side of the film 4 is a second condenser 12,which directs a light beam modulated by the optical sound track 3 onto aline camera 13. In the present exemplary embodiment; the line camera 13contains a CCD line sensor with 512 image sensors. The line camera 13outputs an RS-422 data signal with a word width of 8 bits per pixel. TheRS-422 data signal of the optical sound track 3 passes via a data input14 to a program-controlled data processing device 15.

The data processing device 15 contains a frame grabber 16, whose inputis connected to the data input 14 of the data processing device 15. Anoutput of the frame grabber 16 is connected to a bus system 17. Thefollowing are furthermore connected to the bus system 17: a CPU 18, amemory 19 for program and data storage, an interface 20 with a terminal21 for transferring servo data from and to the film transport servo 11,a video output device 22 with an output terminal 23 for transferring avideo signal to a monitor 24, and an audio output device 25 with anoutput terminal 26 for transferring an audio signal to a loudspeaker 27.

The frame grabber 16 conditions a serial image data sequence of theoptical sound tracks 3, which sequence is generated by the line camera13, buffer-stores it and forwards it with a resolution of 8 bits via thebus system 17 to the memory 19, in which the image data are stored in aRAW file format. The frame grabber 16 has an output 28 for thesynchronization of the line camera 13. In order to limit the datatransfer rate, the scanning frequency of 24 frames per second can bereduced to 6 frames. If the optical sound track 3 is scanned at 2000lines per film frame, a Nyquist frequency of 24 kHz is obtained with afilm transport speed reduced to 6 frames. An amount of 24 Mbytes of datais to be written to the memory 19 per second in this case.

The volume of data supplied by the frame grabber 16 is comparativelylarge. The image data of the optical sound track 3 are therefore writtento a mass storage device, for example to a disk store of the memory 19.The application programs for processing the data of the optical soundtrack 3 and for regulating the film transport are stored in RAM and ROMmemories of the memory 19.

In order to monitor the settings of the illumination source 1 and of theline camera 13 during the scanning operation, the video output device 22is provided, which converts the digital image data of the scannedoptical sound track 3 into an analogue video signal for display on themonitor 24.

For image monitoring of the optical sound track 3, an analogue videosignal can also be tapped off directly from the output of the linecamera 13 and be fed to the monitor 24. It is also possible, of course,to feed the analogue video signal to the input of an oscilloscope (notillustrated) in order to check settings of the luminous flux for maximumsignal levels depending on film density or the focussing and position ofthe line camera 13 with respect to the optical sound tracks 3.

The audio output device 25 serves for listening monitoring. In the audiooutput device 25, the image data of the double variable-area track DZthat are present in the RAW file format are converted into an audio fileformat, e.g. a WAV file format.

In order to couple the scanning frequency of the line camera 13 to thetransport speed of the film 4, the film transport servo 11, whichcontrols the motors of the toothed rollers 9 and 10, is regulated bydata which the data processing device 15 derives in a program-controlledmanner using the image data signal generated by the line camera 13. Theinterface 20 is designed for a bidirectional transfer of data betweenthe film transport servo 11 and bus system 17, so that it is possible toexchange desired and actual data values of the rotational speeds of thetoothed rollers 8 and 9.

As a result of repeated copying of a film onto new film carriers,shading of the homogeneous grey-scale values arises in the event ofinaccurate positioning of the film and/or of the optical copying device.Furthermore, dust particles on the film negative or film positive,during copying, cause dark or bright spots on the optical sound track 3.Moreover, in the event of repeated playback of the film 4, mechanicaldamage in the film running direction can arise; films can also tear. Theoptical sound track 3 of a spliced film 4 may be covered by so-calledsound flies having the form of a triangle, resulting in sounddisturbances. During a copying operation, incident light at locations ofthe perforation or of the film frame can produce periodic brightnessfluctuations which are manifested in a 24 Hz or 96 Hz hum in thereproduced optical sound information.

The pixel data of the optical sound track 3, which are buffer-stored inthe memory 19, are firstly to be subjected to a fixed pattern noise(FPN) correction. Details about this correction can be gathered from theearlier German Patent Application P 100 44 978 6.

In a next processing step, the brightness range of the digital imagesignal generated by scanning the optical sound track 3 is to beoptimized. In this case, data values of the buffer-stored pixels of aplurality of lines, representing brightness values, are subjected, in aprogram-controlled manner, either to a linear or to a nonlinearfiltering. Brightness values of the pixels are altered in such a waythat an erroneous image signal of the double variable-area track, whichimage signal is produced by alternate film densities or alternateillumination, has only image components with constant black and constantwhite.

During the linear filtering, the brightness of extremely bright pixelsis limited. For filtering, the data values of the buffer-stored pixelsof the image signal generated by scanning the optical sound track 3 areadvantageously multiplied by a normalization factor. The normalizationfactor is calculated according to the following equation:Normalization factor=255/bright value

The bright value used in the equation is the average maximum brightvalue of the first 2000 lines in the image signal. The bright value isdetermined by determining in each case the brightest value in 2000lines. An average value is formed from the 2000 brightness valuesdetermined.

The new, changed brightness value of pixels is calculated according tothe following equation:Pixel (new)=Pixel (old)*Normalization factor

During the nonlinear filtering, bright and dark pixels are compressedaccording to a cosine function, average grey-scale values not beinginfluenced. This measure corresponds to edge steepening in an analogueimage signal at black/white transitions.

The nonlinear filter changes brightness values of the pixels accordingto the following equation:

${{Pixel}\mspace{11mu}({new})} = {\frac{255}{2} - {\frac{255}{2} \cdot {\cos( \frac{{P{ixel}}\mspace{11mu}{({old}) \cdot \pi \cdot 2}}{255 \cdot 2} )}}}$

The two-sided edge profile of a double variable-area track determinesthe frequency and the amplitude of the recorded sound information. Inpractice, however, the edge does not comprise an abrupt sudden change inbrightness, but rather a continuous transition from bright to dark, orvice versa. The length of the edge is not constant in this case; itvaries with the frequency and the amplitude of the sound information. Inthe case of line-by-line scanning of the optical sound track 3 by a CCDline camera having 512 pixels per line, the brightness transition of anedge can encompass a range between 8 and 40 pixels.

A distinguishing characteristic for the exact position of the left-handand right-hand edges of the double variable-area track DZ is thepresence of an average grey-scale value in the pixel sequence. In ananalogue image signal, the average grey-scale value would correspond tothe edge centre in a sudden brightness change. The value of the averagegrey-scale value can be calculated line by line as follows:

$\overset{\_}{{White}\mspace{14mu}{value}} = {\frac{1}{\sum\limits_{g = {{{White}\mspace{14mu}{value}} - 20}}^{{{White}\mspace{14mu}{value}} + 20}{{Number}\mspace{11mu}(g)}}{\sum\limits_{g = {{{White}\mspace{14mu}{value}} - 20}}^{{{White}\mspace{14mu}{value}} + 20}{{Number}\mspace{11mu}{(g) \cdot g}}}}$where g corresponds to the grey-scale value.

$\overset{\_}{{Black}\mspace{14mu}{value}} = {\frac{1}{\sum\limits_{g = {{{Black}\mspace{14mu}{value}} - 20}}^{{{Black}\mspace{14mu}{value}} + 20}{{Number}\mspace{14mu}(i)}}{\sum\limits_{g = {{{Black}\mspace{14mu}{value}} - 20}}^{{{Black}\mspace{14mu}{value}} + 20}{{Number}\mspace{11mu}{(g) \cdot g}}}}$${{Grey} - {{scale}\mspace{14mu}{value}}} = \frac{\overset{\_}{{White}\mspace{14mu}{value}} \cdot \overset{\_}{Blackvalue}}{2}$where the white value or black value is a value found in a histogram.

An edge in the double variable-area track is present if the followingcondition is met:

$\begin{matrix}{{\frac{{Pix}_{n - 2} + {Pix}_{n - 1} + {Pix}_{n}}{3} - {Grey} - {{scale}\mspace{14mu}{value}}}} \\{> {{\frac{{Pix}_{n - 1} + {Pix}_{n} + {Pix}_{n + 1}}{3} - {Grey} - {{scale}\mspace{14mu}{value}}}}} \\{< {{\frac{{Pix}_{n} + {Pix}_{n + 1} + {Pix}_{n + 2}}{3} - {Grey} - {{scale}\mspace{14mu}{value}}}}}\end{matrix}$Here, PiX_(n) corresponds to the data value of a pixel at the location nwithin a line.

If the condition is met, a check is supplementarily made to determinewhether the edge is continuous over a region of ±2 pixels. If that isthe case, then an edge pixel and thus the pixel-accurate position of anedge within a scanning line have been found.

Since the centre of an optical sound track does not correspond to thecentre of the recorded double variable-area track due to recordingerrors, the centre of the double variable-area track is calculated lineby line using the two edges in the present exemplary embodiment.

In order to determine the centre of a double variable-area track evenmore accurately, according to the invention the edges are firstlycalculated with subpixel accuracy. In this case, the precise grey-scalevalue is sought around the edge pixels found previously. The new pixellocation is the subpixel-accurate position of an edge. The left-handedge is calculated according to the following equation:

${exactEdgeLeft} = {( {{EdgeLeft} - 1} ) + ( {2*\frac{{Pix}_{{EdgeLeft} - 1} - {Grey} - {{scale}\mspace{14mu}{value}}}{{Pix}_{{EdgeLeft} - 1} - {Pix}_{{EdgeLeft} + 1}}} )}$

In the equation, “Pix” corresponds to the value of the pixel, and“EdgeLeft” corresponds to the location of the pixel.

The right-hand edge is correspondingly calculated with subpixelaccuracy.

If the location of the two edges within a line has been found withsubpixel accuracy, the centre of the double variable-area track can nowalso be calculated with subpixel accuracy. This is done according to thefollowing equation:Centre=(EdgeRight+EdgeLeft)/2

In order to assess the centre more accurately, an ideal centre issubsequently calculated. The ideal centre is averaged over 50 lines,lines which deviate from this ideal centre by a specific value (“ERROR”)not being included in the calculation. In this case, an error isidentified in this line.

FIG. 5 shows, enlarged, a detail from the optical sound track 3 withimage-processed (black) double variable-area track DZ. The detailillustrates the ideal centre M determined—expanded by a factor of10—together with the double variable-area track DZ. The ideal centre Mis depicted as solid centre line. Two further centre lines M_(l) andM_(r) are ±1 pixel remote from the centre M; the further centre linesM_(l) and M_(r) advantageously serve as an evaluation aid. The blackdouble variable-area track DZ with pure tone control RB is bounded by anedge on the left and right.

Measurements have revealed that an edge is not always found, andfurthermore that an edge that has been found is not always correct. Adouple variable-area track has symmetry properties. The two edges of thedouble variable-area track are symmetrical with respect to one another.The property can advantageously be used for restoration purposes by thevariable-area track being mirrored at the centre. A single variable-areatrack is produced in which image errors due to scratches and spots haveonly half the brightness intensity.

If, within a line, an edge of the double variable-area track is notfound or an edge that has been identified is evidently incorrect, theedge of the opposite side is used, instead of the non-found or erroneousedge, for defining the edge position.

In the event of one edge not being identified, the position of the otheredge (position new edge) can be calculated for example according to thefollowing equation:PositionNewEdge=2●IdealCentre−oppositeEdge

An erroneous edge position is identified if the determined centre of thedouble variable-area track deviates from the ideal centre by a specificvalue prescribed by the user.

Erroneous pixels identified in segments of the edge profiles canadvantageously be corrected according to the autocorrelation functiondescribed in the introduction.

In the event of error concealment, pixels which have been identified aserroneous and lie outside the edges of the double variable-area trackare replaced by replacement pixels which have a specific predeterminedgrey-scale value. In order to employ an error concealment measure, theedge end of the double variable-area track should be defined. It shouldbe defined that the edge end must be at a fixed distance from the edgecentre, for example a distance of between 5 and 15 pixels. In the caseof a different definition, it might be defined that, proceeding from theedge centre, that pixel is sought in the case of which the brightnesswith respect to the next pixel remains the same or decreases again.

FIG. 4 shows a flow diagram regarding the above-described measures forprocessing a double variable-area track which is produced by scanning anoptical sound track 3 and is stored as a pixel file with pixel data ofin each case 2000 lines in the memory 19.

In the flow diagram of FIG. 4, at 40, the file—stored in the memory19—with the pixel data of the scanned optical sound track 3 is accessed.At 41, the pixel data are examined to determine whether the two lateralboundaries (edges) of a double variable-area track DZ can be found. Ifit is determined at 42 that only a single edge is present, at 43 thedetermined edge is mirrored to the other side. By contrast, if it isdetermined at 44 that no edge has been found, at 45 the edge of theprevious line is used for further processing. If both edges are present,at 46 the centre of the double variable-area track DZ can be calculated.

In a next step 47, a check is made to determine whether the calculatedcentre deviates considerably from an ideal centre. If that is the case,at 48 a check is furthermore made to determine whether an error ispresent. In the case to the contrary, at 49 the ideal centre iscalculated.

The further course of the signal processing branches depending onwhether an error is present within or outside the track course of thedouble variable-area track DZ. If the error lies within the track courseof the double variable-area track DZ, at 50 an erroneous edge iscalculated anew. However, if the error lies outside the track course ofthe double variable-area track DZ, at 51 the erroneous edge iscalculated anew according to a correspondingly adapted algorithm.Afterwards, at 52 the centre and the edges of the double variable-areatrack DZ are drawn and at 53 a file is created which contains image dataof the double variable-area track DZ and of the edges and the centre.

For reproduction of the sound information recorded on an optical soundtrack 3, the image data now present in processed form in a RAW fileformat are to be converted into audio data of a WAV file format. Theconversion is known per se. In the simplest case, the data values of allthe pixels of each line are summed line by line, subsequently averagedand then converted into an audio data word. The data sequence of theaudio data words generated line by line is transformed into the WAV fileformat. The WAV file of the recorded optical sound information that isgenerated in this way can be decoded via the sound card of a PC and besubjected to D/A conversion into analogue sound information for emissionvia the loudspeaker 24.

The invention has been described using the example of a doublevariable-area track. The use of the apparatus according to the inventiondoes not remain restricted to the reproduction of optical soundinformation in a double variable-area track. It goes without saying thatthe apparatus according to the invention can also be usedcorrespondingly for the reproduction of optical sound informationpresent in single variable-area tracks or multiple variable-area tracks.Furthermore, the apparatus according to the invention can also be usedfor the reproduction of films which have been recorded in a differentfilm format, for example in a 16 mm film format.

1. Apparatus for the reproduction of optical sound recordings, which hasan optoelectronic converter device for the optical scanning of anoptical sound track, which outputs a digital image signal of the scannedoptical sound track at an output, and which contains a device forbuffer-storing the image signal output by the converter device,comprising: a device for the program-controlled data processing of thebuffer-stored image signal, which firstly determines the profile ofedges of a variable-area track from data values of the image signal andwhich then generates audio data for a sound reproduction from data ofthe edge profile determined, wherein, in order to define the edgeprofile of a variable-area track, the data processing device can becontrolled by a program in such a way that the position of suddenbrightness changes within a scanning line is determined by evaluation ofthe distribution of data values of the pixels, representing brightnessvalues.
 2. Apparatus according to claim 1, wherein the data processingdevice can be controlled by a program in such a way that data values ofpixels of a plurality of lines, representing brightness values, aresubjected to a filtering in order to alter specific brightness values ofthe pixels according to a predetermined function.
 3. Apparatus accordingto claim 1, wherein the brightness values of the pixels can be alteredaccording to a linear transfer function.
 4. Apparatus according to claim1, wherein the brightness values of the pixels can be altered accordingto a nonlinear transfer function, in particular according to a cosinefunction.
 5. Apparatus according to claim 1, wherein, for thereproduction of a sound information item recorded in a doublevariable-area track the data processing device can be controlled by aprogram such that, in a first step, the position of edge boundariesrunning transversely with respect to the longitudinal direction of thefilm is determined using the position of sudden brightness changes inthe line profile by evaluation of the data values of the pixels,representing brightness values, that, in a second step, a track centrerunning between the edge boundaries determined is calculated, that, in athird step, the buffer-stored pixel data are mirrored at the calculatedtrack centre, thereby producing pixel data of a single variable-areatrack.
 6. Device according to claim 5, wherein the program of the dataprocessing device is created for the purpose of error detection suchthat, during the evaluation of pixel data of a double variable-areatrack the position region of the track centre is limited by setting anupper and lower threshold.
 7. Apparatus according to claim 6, wherein anovershooting of the upper and/or lower threshold of the position regionof the track centre determined is assessed as an error in the edgeprofile of the double variable-area track.
 8. Apparatus according toclaim 6, wherein the overshooting of a specific boundary in the edgeprofile of the double variable-area track is assessed as an error in theedge profile of the double variable-area track.
 9. Apparatus accordingto claim 5, wherein the program of the data processing device is createdsuch that, in the case of a double variable-area track, the profile ofedge boundaries determined and/or the profile of the track centre issmoothed according to a predetermined function.
 10. Apparatus accordingto claim 1, wherein the program of the data processing device has atleast one test routine for detecting errors in a double variable-areatrack.
 11. Apparatus according to claim 1, wherein the program of thedata processing device has at least one routine for concealing errors ina double variable-area track.
 12. Apparatus according to claim 11,wherein the program of the data processing device is created such that,when errors are detected in pixels of a double variable-area track, theerroneous pixels are replaced by error-free pixels of a preceding lineof the double variable-area track.
 13. Apparatus according to claim 11,wherein the program of the data processing device is created such that,when errors are detected in pixels between edge boundaries of a doublevariable-area track the data value of an erroneous pixel is replaced bythe data value of a black pixel.
 14. Apparatus according to claim 11,wherein the program of the data processing device is created such that,when errors are detected in pixels outside edge boundaries of a doublevariable-area track the data value of an erroneous pixel is replaced bythe data value of a predetermined grey pixel.
 15. Apparatus according toclaim 11, wherein the program of the data processing device is createdsuch that, when errors are detected in pixels outside edge boundaries ofa double variable-area track the data value of an erroneous pixel isreplaced by a data value determined by autocorrelation.
 16. Apparatusaccording to claim 15, wherein, in order to calculate the erroneouspixel in segments of the edge profiles by application of anautocorrelation, firstly the following algorithm is calculated:${a_{before}(n)} = {\frac{1}{a(0)}*\underset{i = 0}{\overset{N - 1}{å}}{g( {y - i} )}*{g( {y - i - n} )}}$where g(y) is a grey-scale value, y is a line number, i is a runningindex from 0 to N-1, n is a variable of the autocorrelation functionwhere n =0 to N-1. N is the number of undisturbed lines to be used forrestoration, and in that erroneous pixels are then replaced bygrey-scale value pixels whose position within a line satisfies thefollowing function:${g(z)} = {{\frac{Z + 1 - z}{Z + 1}*{g( {z - P_{before}} )}} + {\frac{z}{Z + 1}*{g( {z + P_{after}} )}}}$where g(z) denotes a grey-scale value to be replaced. Z denotes thenumber of lines to be replaced, z denotes the line number, 1≦z≦Z,P_(before) and P_(after) denote the periodicities in sound tracks beforeand, respectively, after a detected error.
 17. Method for thereproduction of optical sound recordings, comprising: generating adigital image signal by scanning an optical sound track, buffer-storingdata of the image signal generated, determining an edge profile of avariable-area track recorded on the optical sound track in a mannerdependent on values of the buffer-stored data, and derivingcorresponding audio data for a sound reproduction in a manner dependenton the edge profile determined, wherein, in order to define the edgeprofile of a variable-area track, the position of sudden brightnesschanges within a scanning line is determined by evaluation of thedistribution of data values of pixels, representing brightness values.